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PHP - $_POST


PHP $_POST

$_POST contains an array of variables received via the HTTP POST method.

There are two main ways to send variables via the HTTP Post method:

  • HTML forms
  • JavaScript HTTP requests

$_POST in HTML Forms

A HTML form submits information via the HTTP POST method if the form's method attribute is set to "POST".

To demonstrate this, we start by creating a simple HTML form:

HTML Form

<html>
<body>

<form method="POST" action="demo_request.php">
  Name: <input type="text" name="fname">
  <input type="submit">
</form>

</body>
</html>

When a user clicks the submit button, the form data is sent to a PHP file specified in the action attribute of the <form> tag.

In the action file we can use the $_POST variable to collect the value of the input field.

PHP file

$name = $_POST['fname'];
echo $name;

In the example below we have put the HTML form and PHP code in the same PHP file.

We have also added some extra lines for security.

Example

<html>
<body>

<form method="POST" action="<?php echo $_SERVER['PHP_SELF'];?>">
  Name: <input type="text" name="fname">
  <input type="submit">
</form>

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $name = htmlspecialchars($_POST['fname']);
  if (empty($name)) {
    echo "Name is empty";
  } else {
    echo $name;
  }
}
?>

</body>
</html>
Try it Yourself »

$_POST in JavaScript HTTP Requests

When sending a HTTP request in JavaScript, you can specify that the HTTP method is POST.

To demonstrate this we start by creating a JavaScript function containing a HTTP request:

JavaScript function

function myfunction() {
  const xhttp = new XMLHttpRequest();
  xhttp.open("POST", "demo_phpfile.php");
  xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhttp.onload = function() {
    document.getElementById("demo").innerHTML = this.responseText;
  }
  xhttp.send("fname=Mary");
  }
}

The code above will:

  1. Intiate a HTTP request
  2. Set the HTTP method to POST
  3. Set a valid request header
  4. Create a function to execute when the request is done
  5. Send the HTTP request with a variable fname set to Mary

Look at the function that will be executed when the request is done:

xhttp.onload = function() {
    document.getElementById("demo").innerHTML = this.responseText;
  }

It will try to write a response from the operation in a HTML element with id="demo".

Let us make a HTML page with such element, and also a button that executes the function.

If we also add the the JavaScript, the page looks like this:

Example

How to post and receive data from a HTTP request:

<html>
<script>
function myfunction() {
  const xhttp = new XMLHttpRequest();
  xhttp.open("POST", "demo_ajax.php");
  xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhttp.onload = function() {
    document.getElementById("demo").innerHTML = this.responseText;
  }
  xhttp.send("fname=Mary");
  }
}
</script>
<body>

<button onclick="myfunction()">Click me!</button>

<h1 id="demo"></h1>

</body>
</html>
Try it Yourself »

In the PHP file that receive this HTTP request (demo_ajax.php), we simply use the $_POST variable to retrieve the fname variable, and writes it as a response.

PHP file

$name = $_POST['fname'];
echo $name;